Ailawadhi, Sikander

Abstract Background: Clinical trials are fundamental to advance therapeutics systematically and improve patient outcomes. Despite this, enrollment on clinical trials remains dismal in the United States (US) and is a constant focus of healthcare policy. We studied distribution of clinical trials for B-cell malignancies over time across the US and unique clinical trial opportunities i.e. individual clinical trials for the given diagnosis at a site that patients may have access to participate. Methods: We abstracted data from clinicaltrials.gov for all trials that had non-Hodgkin lymphoma (NHL) or multiple myeloma (MM) as an inclusion indication between 1999-2018. Clinical trial characteristics and distribution over US geographical divisions (West, Midwest, Northeast, and South) were studied, and differences were assessed by Chi-square test. Results: A total of 1930 trials were identified (NHL: 982, MM: 948), of which 483 were recruiting at the time of data abstraction (NHL: 250, MM: 233). Over the past 2 decades, 182691 patients were enrolled on the various trials (NHL: 81592, MM: 101099). Trials by phase of study included phase 1: 629, phase 1/2: 316, phase 2: 813, phase 2/3: 11 and phase 3: 161. Number of trials by phase separated by NHL and MM are shown in Figure 1. Of these, 197 trials were randomized (NHL: 67, MM: 130). Geographical distribution of trials by diagnosis type is shown in Figure 2. A total of 31806 unique trial opportunities were noted for MM and NHL, of which 9,513 were international and 22,293 were in the US, with a geographical distribution of 5080 in West, 8198 in Midwest, 3944 in Northeast, and 5071 in South. 4,883 of the unique trial opportunities were available at NCI/NCCN accredited sites and 17,410 were at non-NCI/NCCN sites in the US. Treatment characteristics of the trials included monoclonal antibodies in 1218, other targeted agents in 2641, stem cell transplant in 526, and other agents in 517 trials with several trials utilizing more than one of these therapeutic options. There was no statistically significant difference in the distribution of clinical trials by phase of study across various US geographical regions for MM (p=0.71), NHL (p=0.98) or combined MM+NHL (p=0.16). On the other hand, unique trial opportunities were significantly different by study phase and geographical distribution for MM, NHL or MM+NHL (all p<0.001) (Figure 3). Conclusions: Widespread access to clinical trials within a cancer diagnosis is imperative for generalizability of trial results. In a comprehensive, national analysis we noted that while it may appear that clinical trials are available across the US, sites where they are open are distributed unevenly, giving rise to a disparity in access to evidence-based therapeutic advancements for patients. Disclosures Ailawadhi: Janssen: Consultancy; Amgen: Consultancy; Pharmacyclics: Research Funding; Takeda: Consultancy; Celgene: Consultancy. Sher:Affimed: Research Funding.

Abstract INTRODUCTION: Patients undergoing HSCT are reported to have a high prevalence of depression and anxiety. These comorbid mood disorders have been known to be associated with alteration in pain perception in patients without hematological malignancies. Pharmacological compounds such as opioid and benzodiazepines are frequently used to manage patient symptomology including pain and anxiety. Patients undergoing HSCT are a unique population where the impact of depression and anxiety on opioid and benzodiazepine use has not been well studied. METHODS: The study population consisted of patients who underwent HSCT at a single center for a variety of hematological malignancies from 2015-2018. Opioid and benzodiazepine exposure and dosage was defined in a) Patients who were exposed to opioid including those who were previously exposed and those who were exposed during hospitalization for HSCT b) Patients who were neither exposed to opioid previously, nor during the hospitalization for HSCT. Depression and Anxiety was defined as per PHQ-9 and GAD-7 scales prior to hospital admission. Multivariable analysis was performed to identify differences in opioid status, previous benzodiazepine use, transplant type, Karnofsky score, gender, age, race, and marital status with associated Diazepam Equivalent Daily Dosage (DEDD) (Negative Binomial Regression), and Morphine Milligram Equivalent Daily Dosages (MMEDD) (Logistic and Zero Truncated Negative Binomial Regression). RESULTS: A total of 275 patients underwent HSCT including autologous and allogeneic from 2015-2018. Anxious or depressed HSCT recipients had an increased incidence of higher DEDD with an IRR of 1.69 (95% CI: 1.15, 2.49) compared to those who were neither depressed nor anxious (Figure 1). However, patients who reported anxiety and depression did not have a different DEDD than those not anxious nor depressed. In addition, patients who were not naïve to benzodiazepine use prior to admission had an increased incidence of a higher DEDD [IRR of 2.23 (95% CI: 1.61, 3.05)]. Patients undergoing autologous stem cell transplant had a decreased incidence of receiving a higher DEDD [IRR of 0.65 (95% CI: 0.47-0.90)]. African American and other populations had a decreased incidence of receiving a higher DEDD [IRR of 0.40 (95% CI: 0.27, 0.59)]. Patients receiving higher MMEDD had a higher DEDD incidence [IRR of 1.01 (95% CI: 1.01, 1.02)]. Patients who were both anxious and depressed had increased odds of receiving an opioid [OR of 3.35 (95% CI: 1.62, 6.94)] compared to patients who were neither depressed nor anxious. However, patients who were either depressed or anxious did not have different odds of receiving an opioid compared to those who were neither depressed nor anxious. Patients undergoing autologous stem cell transplant had reduced odds of receiving an opioid [OR of 0.17 (95% CI: 0.07, 0.40)]. Patients with less than normal Karnofsky performance status (<90 on scale of 1-100) had an increased incidence of receiving a higher MMEDD [IRR of 2.34 (95% CI: 1.07, 5.12)] when modeled by Zero Truncated Negative Binomial Regression. Finally, HSCT recipients who were both anxious and depressed had reduced odds of being naïve to opioids [OR0.31 (95% CI: 0.15, 0.67)] compared to recipients who were neither depressed nor anxious. New opioid users had reduced odds of receiving a greater MMEDD [OR of 0.98 (95% CI: 0.96, 0.99)] when compared to previous users. In addition, autologous stem cell transplant recipients had reduced odds of receiving greater MMEDD compared to allogeneic transplant recipients (OR 0.33, 95% CI: 0.16, 0.66). CONCLUSION: Comorbid depression and /or anxiety impact opioid and benzodiazepine use in patients undergoing HSCT. The presence of these comorbid conditions and their association with increased use of opioids and benzodiazepines can also affect various health related outcomes. Larger studies are needed to fully understand the potential impact of this association on health related outcomes. Figure 1. Figure 1. Disclosures Kharfan-Dabaja: Incyte Corp: Speakers Bureau; Alexion Pharmaceuticals: Speakers Bureau; Seattle Genetics: Speakers Bureau. Ailawadhi:Amgen: Consultancy; Pharmacyclics: Research Funding; Celgene: Consultancy; Janssen: Consultancy; Takeda: Consultancy.

Abstract Abstract 678 Background: Second primary malignancies (SPM) among multiple myeloma (MM) patients have been reported with an estimated incidence varying from 1%–15%. We have previously reported that significant disparity exists in MM survival across patients of different ethnicities. We undertook a Surveillance Epidemiology and End Results (SEER) based analysis to describe the incidence of SPM among MM patients of different ethnicities, in order to explore the variable impact that SPM might have on MM outcomes of patients across racial subgroups. Methods: SEER database was used to examine the standardized incidence rates (SIR) of SPM among MM patients diagnosed between 1973–2008. Observed to expected ratio (O/E) of SPM was calculated using incidence rates of cancers for the general population. The 95% confidence limits (CI) were constructed using Fisher's exact test. The analysis was restricted to patients with MM as first primary, microscopic confirmation of diagnosis, reporting sources not coded as autopsy- or death-certificate-only, and SPM reported more than 2 month after MM diagnosis. Mutually exclusive race/ethnicity categories were: African-Americans (AA), Asians/Pacific Islanders (API), Hispanic whites (HW), Non-Hispanic whites (NHW), and others. The risk of SPM among MM patients was explored by ethnicity, type of SPM, and latency period. Results: A total of 3090 cases of MM with SPM were diagnosed between 1973–2008, of which, 2021 patients met our inclusion criteria. Stratification of SPM by ethnicity revealed: 387 AA (19%), 72 API (4%), 51 HW (3%), 1500 NHW (74%) and 11 other (<1%) cases. There was an average 4.7-year latency period between diagnosis of MM and SPM (mean age 68.2 and 72.9 years, respectively). The latency period was not significantly different by type of SPM (solid organ vs. hematological) or ethnicity. AA had the youngest age at diagnosis for both, MM and SPM (65.6 and 70.1 year, respectively). (Figure 1) For all SPM sites analyzed together, there was no significant difference between the observed and expected incidence (O/E 0.98; 95% CI 0.94–1.02). However, O/E risk was significantly decreased for solid organ SPM (N=1695; O/E 0.92; 95% CI 0.88–0.96) and increased for hematological malignancies (N=263; O/E 1.63; 95% CI 1.44–1.84). Highest excess risk among all SPM was noted for acute non-lymphocytic leukemia (ANLL) (O/E 6.51; 95% CI 5.37–7.83). The overall risk of observed SPM was not different from expected rates by ethnicity, with the exception of HW who had a significantly decreased overall SPM risk. Table 1 summarizes significant results of O/E risk of SPM by race and site. HW and NHW were less likely to develop overall solid organ SPM. Within solid organ sites, HW had a significantly decreased O/E risk of developing lung/bronchus and prostate SPM. NHW were the only ethnic subgroup with an increased O/E risk of developing melanoma of skin, while the O/E risk of developing SPM of kidney/renal pelvis was increased only among AA. The risk of ANLL as SPM was significantly increased among AA, API, and NHW, while risk of NHL as SPM was only increased among NHW. Conclusion: Exploring potential causes of outcome disparities is important for evaluating disease characteristics and optimal triaging of healthcare resources for specific patient populations. We have performed the largest population-based analysis for the risk of SPM in MM patients stratified by race/ethnicity. We found that the risk of developing SPM among MM patients is variable depending on the patient's ethnic background. This warrants further exploration of the impact of SPM on outcomes of MM patients across different racial subgroups. Disclosures: No relevant conflicts of interest to declare.

Abstract Abstract 845 Background: Waldenstrom's macroglobulinemia (WM) is a relatively uncommon plasma cell disorder and most of previous literature is limited to small patient series. We have noted ethnic disparities in multiple myeloma, another plasma cell disorder. We undertook a large Surveillance Epidemiology and End Results (SEER) based analysis to describe outcome disparities in different subgroups of WM patients, with a focus on various ethnicities, so that therapeutic resources can be targeted more effectively. Methods: The SEER 17 Registry data (1973–2008) was utilized for patients with confirmed diagnosis of WM. To avoid bias of under representation of different ethnicities, analysis was restricted to patients with a diagnosis date of 1992 or later. Cases that received a diagnosis at death certificate or autopsy, no follow-up records, as well as lacking documentation on age at diagnosis, sex, or race/ethnicity were excluded. Cox proportional hazards models, adjusted for gender, age, race, year of diagnosis, marital status and stratified by SEER registries were used to evaluate associatio n between patient characteristics and survival. All statistical tests were two-sided and utilized the SAS software (v9.2) with a significance level of 0.05. Results: The final analysis included 2,840 WM patients (1,759 males; 62%, 1,081 females; 38%). The studied age-group cohorts included: 18–64 yrs (845; 30%), 65–74 yrs (795; 28%) and >75 yrs (1,200; 42%). Patients were stratified by race/ethnicity: White (2,471; 87%), African-American (AA) (102; 4%), Hispanic (133; 5%), Asian (129; 5%), and Native American (5; 0.1%). Patients were also stratified based on year of diagnosis (before or after 2002) to study the impact of certain novel agents (proteasome inhibitors, IMiDs) on WM treatment. There was a significant difference in the age at diagnosis of WM patients across different ethnicities, with AA the youngest (median 61.5 years) and Whites the oldest (median 73 years) subgroup (p<0.001). (Figure 1) Cause-specific mortality could not be evaluated due to variable documentation of reported causes of death for WM patients in the database. Survival analysis revealed that for all patients, females had better median overall survival (OS) than males (7.3 years vs. 6.2 years, HR 0.834; 95% CI 0.740, 0.939; p=0.003). Among the different age cohorts, patients with age ≥75 years had a significantly worse median OS (4.1 years) than those 65–74 year-old (7.3 years) or 18–64 year-old (10+ years) (p<0.001). Patients diagnosed after 2002 had a significantly better median OS (7.3 years) as compared to patients diagnosed previously (6.1 years) (p=0.002). Hispanics had the worst median OS (5 years) and Whites had the best median OS (6.8 years) across various ethnicities. In a multivariate model using gender, age, marital status, year of diagnosis and race, a significant interaction was noted between race, age and survival, with Hispanics having a significantly worse OS than Whites (HR 1.86; 95% CI 1.269, 2.726; p=0.003) (Figure 2). Conclusions: Studies of outcome disparities are important for evaluating disease characteristics and management needs of specific patient populations as well as optimal triaging of healthcare resources. We have performed the largest population-based analysis for WM including various ethnicities in the novel therapeutic agent era. We observed that AA patients had a significantly younger age at WM diagnosis. Older patients had worse OS across all ethnic subgroups and patients diagnosed after 2002 had a better OS suggesting an impact of novel therapeutic agents (e.g., proteasome inhibitors, IMiDs). Hispanic WM patients had the worst OS among all ethnicities. This survival difference was more significant and pronounced in patients >75 years. This suggests that the impact of race on survival is influenced by patient's age. These results will help in better understanding of various influences on disease biology and clinical behavior. Disclosures: No relevant conflicts of interest to declare.

Abstract Introduction: With approval of Daratumumab (Dara), targeting CD38 has become an attractive therapeutic option for various B cell cancers including WM. Using preclinical models of WM we investigated CD38 expression patterns, the impact of drug-resistance and the anti-WM effects of Dara, in vitro. An important aspect of our evaluation was the identification of optimal CD38 expression that correlates with maximal cytotoxic effects of Dara; such an approach has not been attempted previously in WM. Methods: WM cell lines (BCWM.1, MWCL.1 and RPCI.WM1) with isogenic proteasome inhibitor-resistant (CR, resistant to carfilzomib, bortezomib and ixazomib) and ibrutinib-resistant subclones (IR) were used. CD38 expression was measured by flow cytometry and a grading system was developed based on increasing CD38 MFI values with 1+= <50,000, 2+ = >50,000 and 3+ = >100,000. Daratumumab-induced specific lysis due to antibody dependent cell cytotoxicity (ADCC) or complement dependent cytotoxicity (CDC) was measured using the Calcein AM assay at an effector to target ratio (E:T) of 100:1. Peripheral blood mononuclear cells (PBMCs) and complement-containing serum were obtained from healthy human donors. Daratumumab, carfilzomib and ibrutinib were obtained from commercial sources. Results: Expression of CD38 (MFI) was highest in RPCI-WM1 (91295.6) > BCWM.1 (13865.3) > MWCL-1 (9804.19) (Figure 1A.). Intriguingly we observed an interesting change in CD38 expression with induction of drug resistance; all CR clones showed a decrease in MFI (RPCI-WM1/CR; øMFI 55960.5 > MWCL-1/CR; øMFI 3890.0 > BCWM.1/CR; øMFI 1381), while decreased expression was noted in all IR clones except one (MWCL-1/IR; øMFI 6272.96, BCWM.1/IR; øMFI 3076 vs. RPCI-WM1/IR; _MFI 461784.6) (Figure 1B). When we applied our CD38 expression grading system, RPCI-WM1/IR cells classified as Grade 3+, RPCI-WM1 and its CR clones as Grade 2+, while all other WM cells were Grade 1+. We noted that utilization of this grading system was helpful in correlating the extent of cytotoxicity to the level of CD38 expression (Table 1). We next treated WM cells with Dara and observed direct lysis in only RPCI-WM1/CR (43%) > BCWM.1/CR (19%) and RPCI-WM1 (11%) cells. However, when Dara-treated WM cells were cocultured with PBMCs, significantly increased ADCC was noted in RPCI-WM1 (90.3%), RPCI-WM1/IR (88.3%) and RPCI-WM1/CR (68.0%) cells (Figure 1C). Although CDC has been reported as a mechanism of mAb-mediated cell death in WM our evaluation of CDC as a potential effector mechanism in daratumumab-treated WM was negative as expected, highlighting ADCC rather than CDC as the primary cytotoxic mechanism. Conclusion: Our analysis of CD38 in WM preclinical models highlights several important findings: 1.) Expression of CD38 changes as WM tumor clones evolve with induction of drug-resistance; an effect that may also be cell-type specific as evidenced by increased CD38 expression in RPCI-WM1/IR cells, 2.) Daratumumab can exert a direct lethal effect in WM cells but this effect is variable and cell line dependent, 3.) Expression of CD38 is an important factor directing cytotoxicity of Dara however antigen density appears to be an important factor and a grading system can be beneficial for future preclinical and/or clinical studies, 4.) ADCC and not CDC appear to be the prominent mechanism of action and 5.) ADCC-mediated cytolytic activity of Dara is contingent on CD38 expression as evidenced by the most specific lysis being noted in CD38 Grade 2+ and 3+ expressing WM cells (Table 1.). These observations can help direct optimal design of clinical studies with Dara in WM where drug resistance and CD38 expression should be further explored as factors contributing to the clinical efficacy of this new agent. Disclosures Ailawadhi: Pharmacyclics: Consultancy; Novartis: Consultancy; Amgen Inc: Consultancy; Takeda Oncology: Consultancy. Ansell:BMS, Seattle Genetics, Merck, Celldex and Affimed: Research Funding.

Abstract Background WM remains an incurable cancer despite recent advances. While a phase II trial has demonstrated efficacy of dexamethasone, rituximab and cyclophosphamide (DRC) in the treatment-naïve (TN) patients, this regimen has not been studied systematically in the relapsed/refractory (R/R) setting. Recent data has suggested the MYD88mutation status in WM patients can serve as a predictive marker with therapies such as ibrutinib. We examined the efficacy and tolerability of up to 6 cycles of DRC, with focus on R/R population and activity of this regimen with respect to the patients' MYD88L265Pstatus. Methods Records of WM patients seen consecutively at Mayo Clinic campuses in Rochester, Arizona and Florida from 01/2007 to 12/2014 were reviewed. MYD88L265P status, as assessed by AS-PCR, was recorded when available. Data obtained from symptomatic patients treated with DRC (dexamethasone 20 mg intravenously followed by rituximab 375 mg/m2 intravenously on day 1 and cyclophosphamide 100 mg/m2 orally bid on days 1 to 5) were analyzed. Time-to-event analyses were performed from DRC therapy using the Kaplan-Meier method. We used the Consensus response criteria (6th International Workshop). Results Of 100 symptomatic patients who received DRC, 50 had R/R WM (40% refractory) and 50 were TN. Table 1 shows the patients' baseline characteristics. In the R/R population, DRC was 2nd line (range 2-8) therapy in 58% of patients. The median IgM levels declined from 3,870 mg/dL to 1,846 mg/dL (p=0.0001) at best response. Median follow-up from DRC was 51 months (95% CI: 38-55). The median time-to-best response was 6.8 (0.5-28) months. Overall response rate (ORR) was 87% [VGPR 4%, PR 64%, MR 19%]. Four patients (9%) achieved SD and 2 patients (4%) had PD. Of the sixteen deaths (32%) noted at time of analysis, 11 were related to progressive disease. The median disease-specific survival (DSS) from DRC was not reached (NR) (95% CI: NR-NR). The median progression-free survival (PFS) and time-to-next-therapy (TTNT) were 32 months (95% CI: 15-51) and 50 months (95% CI: 35-60), respectively. In contrast, in the TN patients the median IgM levels declined from 4,130 mg/dL to 1,250 mg/dL (p=0.0001) at best response; median time to best response was 11 (0.6-47) months; median follow-up from DRC was 30 months (95% CI: 21-36). ORR was 96% [VGPR 17% (n=8), PR 70% (n=32), MR 9% (n=4)]. Of the 7 deaths (14%) at time of analysis, 4 were related to WM progression. Median DSS from DRC was NR (95% CI: NR-NR); median PFS and TTNT were 34 months (95% CI: 23-NR) and NR (95% CI: 37-NR), respectively. Among 29 genotyped patients in whom MYD88 mutation status was available, MYD88L265P was present in 25 patients (8 of 10 TN and 17 of 19 R/R patients). The response rates and the time-to-event outcomes were similar in the MYD88L265P and wild-type patients. Grade ≥3 adverse effects included neutropenia (20%), thrombocytopenia (7%) and infections (3%). Conclusions Similar to the frontline setting, DRC is an active and well-tolerated salvage regimen. In contrast to ibrutinib, DRC offers a less expensive, limited-duration treatment option, with preliminary data suggesting activity independent of patients' MYD88 mutation status. Disclosures Ailawadhi: Pharmacyclics: Consultancy; Novartis: Consultancy; Amgen Inc: Consultancy; Takeda Oncology: Consultancy. Kumar:Glycomimetics: Consultancy; Sanofi: Consultancy, Research Funding; Noxxon Pharma: Consultancy, Research Funding; Onyx: Consultancy, Research Funding; AbbVie: Research Funding; Celgene: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Millennium: Consultancy, Research Funding; Kesios: Consultancy; Array BioPharma: Consultancy, Research Funding; Skyline: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Consultancy. Dispenzieri:Jannsen: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; pfizer: Research Funding; Celgene: Research Funding; Prothena: Membership on an entity's Board of Directors or advisory committees; Alnylam: Research Funding; GSK: Membership on an entity's Board of Directors or advisory committees. Ansell:BMS, Seattle Genetics, Merck, Celldex and Affimed: Research Funding. Kapoor:Amgen: Research Funding; Celgene: Research Funding; Takeda: Research Funding.

Abstract Background: Aberrant B-cell receptor (BCR) and MYD88 signaling cooperatively drive Waldenstrom macroglobulinemia (WM) tumor cell survival. To sustain BCR-driven growth and maintain optimal cellular homeostasis, WM cells upregulate proteasome function. We have recently described the role of two distinct 19S proteasome-associated deubiquitinating enzymes (DUBs), USP14 and UCHL5, in maintaining WM-cell viability. Pharmacologic inhibition with b-AP15 (commercial compound) results in WM-cell death and accumulation of high molecular weight ubiquitinated protein conjugates; an event that is phenocopied by siRNA knockdown of USP14 and UCHL5. VLX1570 is a lead-optimized clinical grade analog of b-AP15 with enhanced solubility, stability and target residence time. We investigated the effect of VLX1570 on BCR components, WM cell survival proteins and its in vivo activity in a human xenograft model of WM. Materials: VLX1570 was obtained from Vivolux AB and bortezomib from Sellekchem. Human WM cell lines (BCWM.1, MWCL-1 and RPCI-WM1) and their drug-resistant derivatives were used (total n=12). Bone marrow aspirates from WM-patients and from healthy donors were obtained from the Mayo Clinic biospecimens core. PBMCs from healthy donors were used as comparators where needed. NOD/SCID mice were obtained from Taconic Labs and used for profiling the in vivo properties of VLX1570. Results: We first examined for USP14/UCHL5 protein expression by immunohistochemical analysis in primary tumor tissue from WM patients and compared it to healthy donor cells. WM patient-derived cells exhibited greater staining intensity of both DUBs. Preferential binding of VLX1570 to USP14 and UCHL5 in WM cells was probed in a WM cell using an enzyme-based competition assay (HA-Ub-Vs), which demonstrated time-dependent decrease in labeled USP14 and UCHL5 after treatment with VLX1570. In drug-resistant (bortezomib or ibrutinib-resistant) WM cells, VLX1570 induced >50% tumor-specific apoptosis and displayed synergistic activity with ibrutinib (median CI: 0.5). In addition to ER stress markers, we had previously observed that gene expression of BCR-signalosome components were reduced in VLX1570-treated WM cells (NanoString platform) and this was substantiated at the protein level where p-SYK, SYK and BTK decreased in a time-dependent manner. BCR end-effectors were probed in response to VLX1570 and a decrease in nuclear translocation of NFkB (p65) was noted. USP14 has been shown to control the availability of the chemokine receptor CXCR4, which regulates homing of WM cells to bone marrow. After VLX1570 treatment, we noted a significant decrease in CXCR4 surface receptor expression in all WM cell lines tested and primary WM cells. Lastly, to determine the in vivo anti-WM effects of VLX1570, we injected NOD/SCID mice (xenotransplanted with RPCI-WM1-Luc cells) with VLX1570 (I.P. route, 4.4mg/kg every other day) and measured tumor burden along with pharmacodynamic indicators. VLX1570-treated mice (n=7) demonstrated significantly lower tumor volumes by caliper measurement and bioluminescent signal (p=0.01 - 0.003) as well as reduced serum human-IgM, compared to vehicle-treated mice (n=7). Importantly, mice treated with VLX1570 survived longer vs. vehicle-treated mice (median survival, 62 vs. 44 days, respectively, p=0.0008). No unforeseen toxicities were noted and weight of the mice in vehicle vs. VLX1570-treated mice did not significantly change. IHC analysis in mice tumor tissues demonstrated reduced CXCR4, human-IgM, Ki67 and increased cleaved caspase-3 and ubiquitinated (k48-linked) protein level, the latter serving as a more specific indicator of USP14/UCHL5 inhibition. Conclusions: We provide substantial in vitro and in vivo evidence on the anti-WM effects of a novel first-in-class clinical grade USP14/UCHL5 inhibitor, VLX1570. In addition to anticipated induction of ER stress machinery, we describe for the first time VLX1570-mediated modulation of BCR components and WM cell survival proteins as well as demonstrate its robust activity in an aggressive human xenograft model of WM. These data provide the rationale for a clinical trial of single agent VLX1570 in patients with symptomatic WM. Disclosures Martin: Janssen: Consultancy, Honoraria; Acerta: Consultancy; Gilead: Consultancy; Celgene: Consultancy; Novartis: Consultancy; Bayer: Consultancy. Gullbo:Vivolux AB: Other: Shareholder. Linder:Vivolux AB: Other: Shareholder.

Abstract Background Waldenstrom macroglobulinemia (WM) is an IgM-associated lymphoplasmacytic lymphoma, first described over seven decades ago. Although WM is typically a disease of the elderly, with a median age at diagnosis of ~ 67 years, approximately 10% of patients are ≤50 years (y) of age at diagnosis. Data for young patients are sparse and the few available studies demonstrate inconsistent findings, with potential overestimation of survival owing to inclusion of patients with smoldering WM. In this case-control study, we evaluate outcomes, prognostic features and impact of changing therapies in a large cohort of young symptomatic WM patients compared to matched older patients seen over the course of the past five decades. Methods The medical records of all WM patients seen consecutively at Mayo Clinic from 01/1960 to 10/2013 were reviewed. Of 1181 patients, 140 (11.8%) were ≤ 50 y of age at diagnosis. A cohort of patients 65 y or older at diagnosis, matched 1:1 by the time of diagnosis, served as the control population. The patients were divided into 3 groups based on the timing of initiation of therapy: Group 1 (1960-1977), Group 2 (1978-1995) and Group 3 (1996-2013). The baseline characteristics were compared. Initiation of frontline therapy was used for all time-to-event analysis using the Kaplan Meier method. Results Younger patients were more likely to present with adenopathy and splenomegaly, have higher IgM levels and hyperviscosity symptoms (Table 1). The median follow-up from the frontline therapy was similar (10.7 y vs. 10 y for the control population). At the time of analysis, 91% of the deaths for the younger cases were WM-related compared to 58% in the control arm (p=0.0001). Younger patients had a better OS with a median disease-specific survival (DSS) of 15.6 y (95% CI: 13-21; 10-y OS of 77%) vs. 11 y (95% CI: 7.8-12; 10-y OS of 51%) for the older patient (p=0.0003). Among the young patients, there was no difference in the median DSS across the 3 groups (p=0.42). However, the median DSS for the control group incrementally improved (p=0.02) over the 3 time periods (Table 1). In the younger patients, no improvement in DSS was noted with the use of either frontline rituximab-based therapy compared to non-rituximab based regimens [median NR (95% CI: 7.6-NR) vs. 15.8 y (95% CI: 13-22) with other regimens, p=0.30], or frontline chlorambucil-based compared to non-chlorambucil based regimens [median 16 y (95% CI: 12-22) vs 15.6 y (95% CI: 12-NR) with other regimens, p=0.73]. In the control group, however, there was significant difference in DSS among patients who received frontline rituximab-based compared to non-rituximab based regimens [median NR (95% CI: 8.3-NR) vs 9.1 y (95% CI: 5.6-12) with other regimens, p=0.04], or frontline chlorambucil-based vs non-chlorambucil based regimens [8 y (95% CI: 5-12) vs 12.3 y (95% CI: 11-NR) in other regimens; p=0.001]. Conclusion Striking differences in presentation are evident in young WM patients compared to their older counterparts. The incorporation of rituximab to the previously existing anti-WM regimens and the transition to non-chlorambucil based regimens has resulted in substantial survival gains in the older WM population over the past five decades. However, such improvement in outcome has not yet been observed in the young patients. The majority of younger patients, despite a protracted disease course, succumb to their disease. Disclosures Ansell: BMS, Seattle Genetics, Merck, Celldex and Affimed: Research Funding. Ailawadhi:Pharmacyclics: Consultancy; Novartis: Consultancy; Amgen Inc: Consultancy; Takeda Oncology: Consultancy. Reeder:Novartis: Research Funding; Celgene: Research Funding; BMS: Research Funding; Millennium: Research Funding. Kumar:Kesios: Consultancy; Janssen: Consultancy, Research Funding; Sanofi: Consultancy, Research Funding; AbbVie: Research Funding; BMS: Consultancy; Onyx: Consultancy, Research Funding; Glycomimetics: Consultancy; Millennium: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Noxxon Pharma: Consultancy, Research Funding; Array BioPharma: Consultancy, Research Funding; Skyline: Honoraria, Membership on an entity's Board of Directors or advisory committees. Dispenzieri:Alnylam: Research Funding; Celgene: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Prothena: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees; pfizer: Research Funding; Jannsen: Research Funding. Kapoor:Celgene: Research Funding; Takeda: Research Funding; Amgen: Research Funding.

Abstract Background Bendamustine/rituximab (BR) and dexamethasone/rituximab/cyclophosphamide (DRC) combination therapy are acceptable options for the treatment of WM, both in the frontline or salvage setting. Prospective data, however, are only available in treatment-naïve (TN) WM patients, and no direct comparison between BR and DRC has been reported. We compared outcomes of BR and DRC in relapsed/refractory (R/R) and TN WM patients seen at a single institution. Methods Records of WM patients seen consecutively at Mayo Clinic from 01/2007 to 12/2014 were reviewed. The MYD88L265P status, as assessed by AS-PCR, was recorded when available. The data obtained from symptomatic patients treated with DRC or BR were analyzed. The time-to-event analyses were performed from DRC or BR therapy using the Kaplan-Meier method. We used the Consensus criteria (6th International Workshop) for response assessment. Results Of 160 WM patients, 60 patients received BR (73% in R/R setting) and 100 patients received DRC (50% in R/R setting). In the R/R population, BR was the 2nd line (range 2-11) therapy in 47% of patients, while DRC was 2nd line (range 2-8) in 58% of patients. Rituximab monotherapy was the only prior line of therapy in 8 (20%) patients in the BR group and 20 (40%) in the DRC group (p=0.66). Baseline characteristics were similar in patients treated with BR or DRC (Table 1). Six patients received both BR and DRC during their disease course and overlapped between the 2 cohorts. Among the previous untreated patients, the median IgM levels decreased from 3,785 mg/dL to 724 mg/dL (p=0.0001) at best response with BR, while it decreased from 4,130 mg/dL to 1,250 mg/dL (p=0.001) with DRC. The median time to best response was 6.1 (1-25) months in the BR group and 11 (0.5-47) months in the DRC group (p=0.13). For patients treated with BR, the overall response rate (ORR) was 93% [VGPR 29% (n=4), PR 57% (n=8), MR 7% (n=1)]. One patient (7%) had progressive disease. For patients treated with DRC, ORR was 96% [VGPR 17% (n=8), PR 70% (n=32), MR 9% (n=4)]. One patient (4%) achieved SD. Median follow up in the BR and DRC groups were similar (30 months). The 2-year progression-free survival (PFS) was 88% and 61% in the BR and DRC groups, respectively (p=0.08). The 2-year time-to-next therapy (TTNT) was 88% and 76% in the BR and DRC groups, respectively (p=0.35). Median PFS, TTNT and disease specific survival (DSS) were not reached with either regimen. In the R/R setting, the median IgM levels decreased from 3,880 mg/dL to 659 mg/dL (p=0.0001) at best response with BR, and from 3,870 mg/dL to 1,846 mg/dL (p=0.001) with DRC. The median time to best response was similar [7 (1-39) months with BR and 7 (0.5-28) months with DRC (p=0.77)]. For patients treated with BR, ORR was 95% [CR 3% (n=1), VGPR 38% (n=14), PR 41% (n=15), MR 13% (n=5)]. Two patients (5%) had progressive disease. With DRC, the ORR was 87% [VGPR 4% (n=2), PR 64% (n=30), MR 19% (n=9)]. Four patients (9%) achieved SD and 2 patients (4%) had progressive disease. Median follow up from BR was 32 months and 51 months from DRC (p=0.24). The 2-year PFS was 66% and 53% in the BR and DRC groups, respectively (p=0.08). The 2-year TTNT was 75% and 68% in the BR and DRC groups, respectively (p=0.24). The median DSS in the BR group was 69 months (95% CI: 65-69) and NR (95% CI: NR-NR) in the DRC group (p=0.57). The proportion of patients with R/R disease was significantly higher in the BR cohort (Table 1). In a bivariate analysis of the entire cohort for PFS, incorporating the setting (TN vs. RR) and the regimen involved (BR vs. DRC), the latter emerged as a significant factor (hazard ratio 0.52, p=0.019) in favor of BR. Time-to-event outcomes and response rates were similar in the MYD88L265P and MYD88WT patients. Grade ≥ 3 adverse events were neutropenia (12%), infections (7%) and nausea/vomiting (2%) with BR, and neutropenia (20%), thrombocytopenia (7%) and infections (3%) with DRC. Conclusions Although both DRC and BR regimens show activity and comparable toxicities, BR regimen shows a trend for superior PFS in WM patients, both in the TN and R/R setting. No difference was seen in TTNT. MYD88 L265P mutation status does not appear to impact activity of BR or DRC. Randomized controlled trial(s) are needed to confirm our findings. Disclosures Ailawadhi: Pharmacyclics: Consultancy; Novartis: Consultancy; Amgen Inc: Consultancy; Takeda Oncology: Consultancy. Ansell:BMS, Seattle Genetics, Merck, Celldex and Affimed: Research Funding. Reeder:Millennium: Research Funding; BMS: Research Funding; Novartis: Research Funding; Celgene: Research Funding. Dispenzieri:Jannsen: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; pfizer: Research Funding; Prothena: Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; Alnylam: Research Funding; GSK: Membership on an entity's Board of Directors or advisory committees. Kumar:Sanofi: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; AbbVie: Research Funding; Array BioPharma: Consultancy, Research Funding; BMS: Consultancy; Kesios: Consultancy; Glycomimetics: Consultancy; Skyline: Honoraria, Membership on an entity's Board of Directors or advisory committees; Noxxon Pharma: Consultancy, Research Funding; Millennium: Consultancy, Research Funding; Onyx: Consultancy, Research Funding; Celgene: Consultancy, Research Funding. Kapoor:Celgene: Research Funding; Takeda: Research Funding; Amgen: Research Funding.

Abstract Background: Mitochondrial activity is critical to maintain a high cellular proliferation especially in drug-resistant clones. Ibrutinib-resistance (IR) in CLL is associated with highly aggressive clinical behavior, carrying a median survival of ~3 months. While these outcomes are not yet reported in WM, resistance to ibrutinib is foreseeable considering no WM patients achieve a complete remission with BTK inhibitors (reported series). The transition to a highly proliferative drive in the IR clone remains a biological dilemma and understanding this will allow rationale development of therapeutic strategies. It is established that increased cell proliferation is highly dependent on the functional capabilities of the mitochondria. Yet the respiratory proficiencies and adaptation of mitochondrial machinery in the IR state remains unknown. Here we interrogated mitochondrial function and its relevance in IR cells using our WM models. Materials: WM cell lines (BCWM.1, non-IR) and its isogenic IR clone (BCWM.1/IR; 20-fold resistant, without BTK or CXCR4WHIM-like mutations) were used. Mitochondrial respirometry was measured by Seahorse XF96 flux analyzer (Fig. 1a). Drug sensitivity and cytotoxicity were determined by Cell-Titer Glo cell viability assay. Whole exome sequencing (WES) was performed on an Illumina HiSeq2000. Results: IR WM cells were noted to be in G1 arrest with altered morphologic features and growth kinetics. Despite growth arrest, IR cells showed increased basal oxygen consumption rate (OCR) (>30% increase) vs. parental (non-IR) cells. Consistent with this we observed enhanced mitochondrial ATP production suggesting increased mitochondrial utilization by the IR clones. We then measured maximal respiratory potential of WM cells with FCCP pre-treatment, which evaluates cellular potential to respond to increased ATP demand. We observed upregulation of mitochondrial spare respiratory capacity in BCWM.1/IR cells vs. parental BCWM.1 cell. In addition, a >50% increase in non-mitochondrial oxygen consumption/respiration was also noted (Fig.1b, c). To identify potential genomic changes that could explain mitochondrial overdrive, WES of the non-IR and IR cells was performed. Interestingly, this analysis did not uncover any mutational alterations in genes directing cellular oxidative phosphorylation (NDUF, COX1, COQ7, SURF1, etc.), glycolysis (PDK1, HK2, PKM2, ALDOA, etc.) or ATP production (ATP5, ND1, UCP1 and others). We then asked if mitochondrial function impacts therapeutic potential of a specific drug (or a class of drug), focusing specifically on proteasome disruption. First, we observed that proteasome inhibition- independent of the site (20S vs. 19S), retained high cytotoxic potential, wherein IR cells showed exquisite sensitivity to proteasome disruption. Interestingly, VLX1570 (targets 19S proteasome) had a 2-fold lower IC50 in IR clones than its non-IR counterpart. Cell respirometry demonstrated that compared to parental cells, VLX1570 (500nM) treatment significantly (p<0.002) and rapidly (2hr) attenuated basal respiration in IR clones at concentrations half of those needed to achieve similar effects in BCWM.1 cells. A concomitant decrease in ATP production as well as spare respiratory capacity was observed at these time points/drug concentrations (significantly more evident than in BCWM.1 cells). While our focus was mitochondrial bioenergetics and its therapeutic relevance in drug-resistant WM, unexpectedly we observed for the first time, evidence that VLX1570 induces changes in mitochondrial bioenergetics as early as 2hrs leading to increased mitochondrial membrane permeability and cell apoptosis in 6-12hrs. Comparable observations were made with bortezomib (targeting 20S). Conclusions: This is the first report identifying the role of mitochondrial hyper-drive in WM cells with resistance to ibrutinib. Of note, enhancedmitochondrial bioenergetics in the IR state increased sensitivity to proteasome inhibition and this was independent of the site of disruption in the proteasome pathway. Although, WES findings alone were not sufficient in explaining mitochondrial overdrive noted in our system, ongoing analysis of various mitochondrial functions (Fig. 1d) at the gene expression, copy number and epigenetic level may elucidate the underlying biomechanics of mitochondrial disposition in IR WM cells. Disclosures Ansell: BMS, Seattle Genetics, Merck, Celldex and Affimed: Research Funding. Linder:Vivolux, Ab: Other: Shareholder. Ailawadhi:Pharmacyclics: Consultancy; Novartis: Consultancy; Amgen Inc: Consultancy; Takeda Oncology: Consultancy.